Above all ... R.T.F.M.

I have been struggling, for some considerable time, to do a bit of focus-stacking. They're not so much "stacked" as piled up together, but there you go.
Problem 1. After adding them all and clicking Merge, I ended up with a shot indistinguishable from one of the "X" previous shots.
Finally I got around to re-watching the Youtube© clip and realised there was a step which hadn't sunk in to the mental software.

NEXT step ... Manage a sufficient number of D.o.F. that there are no fuzzy spots, however, I'm fair to middling chuffed that
A) I finally managed an, albeit puny, first attempt at stacking.
B) I've, finally grasped(?) another fraction of PhotoShop©.